The invention relates to a cooking apparatus in which the cooking is effected by irradiating a material to be cooked with microwave radiation, and more particularly to a microwave cooking apparatus in which a scorched texture is effectively produced on the material to be cooked.
Generally, when cooking with a microwave oven, no scorching appears on the surface of a material to be cooked in view of the nature of heating which takes place only internally of the material. However, the scorching is often necessary to suit the taste because the absence of scorching when roasting or broiling a fish results in an appearance that the fish remains raw or undone and such absence of gratin diminishes its taste. These considerations led to the use of scorching means concurrently with the cooking of a material in a microwave oven, which means heretofore comprised (1) incorporating an infrared or nichrome wire heater within the microwave oven, (2) using a dish comprising ferrite or silicon carbide ceramics as a microwave absorbing, heating element, (3) flame spraying a resistive film to the rear surface of a heat-resisting glass with supporting metal legs attached thereto, (4) placing a material to be cooked on a microwave absorbing heating element which is provided with metal antennas, (5) placing a material to be cooked which is enclosed by an aluminium foil on the heating element, or the like.
However, these techniques involve various drawbacks which are mentioned below. Specifically, the technique (1) must upgrade the power capacity of the microwave oven to effect the heating by microwave radiation concurrently with the scorching by the heater or must tolerate the heating by the microwave radiation followed by the scorching with the heater. However, the general house wiring from the distribution line may not accommodate for the required power in the former case, which must be supplemented by an additional wiring work to the kitchen, dining room or other location of the customary household where the microwave oven is located. In the latter case, the labor and time required for the cooking are doubled. In addition, the scorching cannot be achieved with a microwave oven which is not provided with a heater. Furthermore, the cool cooking which characterises the usual microwave oven is no longer possible, thus rendering the use of paper napkin, plastic receptacle or the like impossible. The entire interior of the oven is substantially heated, so that the interior structure of the oven must be made of refractory material. Furthermore, there is the possibility for oil from the material to be cooked such as meat or fish to be sputtered around. The technique (2) utilizes the fact that a dish formed of ferrite or silicon carbide ceramic produces a great deal of heat when subjected to microwave radiation, but has a general tendency to absorb the moisture, or to retard the generation of heat due to its absorption of microwave radiation when it is co-existent with a material to be cooked, as compared with when such material is left alone, thereby requiring a considerably increased length of time until a temperature is reached at which a scorching appears on the surface of a material to be cooked. If such an increased period of time is allowed for the purpose of scorching, there arises the likelihood that the material to be cooked is excessively internally heated or becomes dried up. To avoid these likelihoods, it is necessary to pre-heat the heating element alone before a material to be cooked is placed in contact therewith for the purpose of microwave heating, which however renders the cooking procedure complicate. In addition, there is also the possibility that a detergent or oil contained in a material to be cooked may become absorbed into the heating element, or conversely harmful metals within the heating element may become mixed with the material to be cooked. The technique (3) involves the disadvantages that the resistive film is susceptible to mechanical detachment, that the supporting metal legs may cause a hazardous spark discharge upon contact with the inner surface of the oven to thereby damage it, and that it often requires a pre-heating without the material as in the technique (2). The fourth technique is also susceptible to the occurrence of a hazardous spark discharge upon contact of the antenna with the inside of the oven to damage it, and also often requires a pre-heating of the heating element alone. Finally, the fifth technique, while it permits a certain degree of control over the heating and/or the suppression of drying up without recourse to pre-heating by virtue of the partial shielding effect of the microwave radiation provided by the aluminium foil, suffers from poor reproducibility, and does not assure the re-use of the aluminium foil. In addition, the aluminium foil may cause a spark discharge within the oven.
Therefore, it is an object of the invention to provide a microwave cooking apparatus capable of scorching a material to be cooked and which is hygienic and safe in operation.
It is another object of the invention to provide a microwave cooking apparatus capable of scorching the surface of a material to be cooked without excessively heating the interior of the material.
It is a further object of the invention to provide a microwave cooking apparatus which permits the scorching of the surface of a material to be cooked with minimized labor and without requiring a pre-heating of the heating element alone.
It is an additional object of the invention to provide a microwave cooking apparatus which can be used in the general household without requiring a special house wiring.
It is still another object of the invention to provide a microwave cooking apparatus capable of scorching the surface of a material to be cooked and which is safe and insusceptible to a spark charge and damage.
It is a still further object of the invention to provide a microwave cooking apparatus which enables the control over both the internal heating of a material to be cooked and the degree of scorching of the surface thereof.